The present invention relates to optical switching systems for optical fiber communication and optical information processing systems, and more particularly to wavelength insensitive, scalable mxc3x97n optical switching networks which facilitate high capacity, high speed, high extinction ratio optical signal switching.
The advent of the internet has prompted a tremendous surge in demand for bandwidth to accommodate large volumes of data traffic that travels through service providers"" networks. Optical transmission systems potentially offer a basis for communications networks of very high capacity capable of handling such traffic. The capacity of such systems is envisioned to be used to provide internet connections for large numbers of systems to high bandwidth services such as high bit rate data communications, video on demand, video telephony, etc. A major constraint on the performance of such high capacity networks, however, is the current switching technologies. The structures of such switching networks tend to be predominately electronic and are therefore limited to capacity considerably lower than those which can be achieved in the optical domain. Typically, operation of an electronic switch in an optical domain requires that the optical signal from one of m optical input fibers be first converted to an electrical signal and then directed to any one of n output ports of the switching network by electrical circuitry. The electrical signals at the output port are then converted back into an optical signal for transmission through fiber optic cables. The conversion of the optical signal to an electric signal and then back into an optical signal, together with electrical switching circuitry, requires the use of expensive components and restricts the potential bandwidth of the communication network.
xe2x80x9cAll-opticalxe2x80x9d systems have been widely proposed for optical communication systems. In all-optical systems, the optical signals are intended to propagate in the form of light through the transmission path, the multiplex/separation circuit, logic circuits, and the like within the system while not being subject to a light to electric signal conversion or an electric signal to light conversion during the propagation. In such systems, the switches are intended to be capable of directly switching an optical signal. That is, the switches are intended to be capable of switching the optical signal from one of m optical input fibers to any one, of n optical output fibers without converting that signal to an electrical form.
Current optical switch designs have their drawbacks. For example, current two-dimensional (2-D) architecture waveguide based switches tend to require additional arrayed wave guides (AWG) and, thus, crossing nodes to couple incoming incident beams back into output fibers because the total internal angles from input ports to output ports tend to be very small. As a result, 2-D waveguide based switches tend to experience excess loss and cross talk across the additional crossing nodes, and tend to be slow in speed and expensive to manufacture. Other optical switches that employ moving parts, as in bubble technology, tend to lack reliability. Current three-dimensional (3-D) switches employing a vertical 3-D architecture tend to comprise an excessive amount of components in multiple levels and, as a result, tend to be complex to operate and very expensive and complex to manufacture. 2-D and 3-D switches based on micro electro-mechanical systems (MEMS) tend to employ a great deal of moving parts and electronic components, and inherently suffer from reliability problems, tend to have slow response times, and are complex and expensive to manufacture.
Thus, it would be desirable to provide an all-optical switch that is scalable, has low losses, provides high speed, high capacity switching at high extinction ratios, is mechanically simple, and is long lasting.
The present invention is directed to an improved optical switch having a three dimensional architecture that facilitates high speed, high capacity switching at high extinction ratios and low losses, and is mechanically simple, scalable and reliable. In one innovative aspect, the switch of the present invention advantageously takes input optical signals (incident beams) launched in a first direction, e.g., an x-direction, and then deflects the signals in a second direction, preferably 90-degrees in a z-direction, and then again in a third direction, preferably orthogonal to the first direction, i.e., 90-degrees in a y-direction, with no moving parts. After being deflected in a third direction, the signals propagate through xe2x80x9cfree spacexe2x80x9d and are advantageously directly collected into output fibers at an elevated level without passing through additional nodes and incurring additional losses.
In a preferred embodiment, the switch includes a first layer comprised of a series of (n) Faraday rotator bars interlaced with a series of (n) vertically oriented beam splitter bars. The beam splitter bars and rotator bars are oriented in parallel relation with one another and extend longitudinally along axes that are parallel to the y-axis or output axes of the switch. An array of (n2) electrode pairs are selectively deposited on the top and bottom of the rotator bars to form a matrix of (n2) electro-optic (E-O) or electro magneto optical (EMO) polarization rotator elements within the first layer of the switch. A second layer, positioned above the first layer and formed from a substrate such as silicon, glass, quartz or metal, and the like, preferably comprises a series of (m) 45-degree sloped stepped surfaces that extend longitudinally along axes that are parallel to the x-axis of the switch. Passive mirrors are mounted on the stepped surfaces and optically aligned with each row of the matrix of electro-optic (EO) or electro mangeto optical (EMO) rotator elements in the first layer. The switch further includes input and output channel arrays having input and output fibers and collimating, polarizing and focusing optics.
In operation, when voltage is applied to an E-O or EMO rotator element, the element shifts the phase 90-degrees of a beam incoming along an x-axis. The phase shifted beam then passes vertically through the beam splitter bar and migrates along a z-axis toward the second layer where it hits a passive mirror and is turned 90-degrees. The turned beam then migrates through free-space along the y-axis and is coupled into an output fiber after passing through a focus lens.
In an alternate embodiment, the optical switch of the present invention includes a second layer having a parabolic mirror surface formed on its underside. Output focusing optics may advantageously be eliminated because the geometry of the parabolic surface enables the beam to be directly coupled into an output fiber by a micro mirror.
In another alternate embodiment, the vertically directed beams may be locally coupled into output fibers directly above the beam splitter bars after passing through focus lenses or an array of collimating micro-lenses.
In another innovative aspect of the present invention, the switch includes a wave guide based 3-D architecture. The switch advantageously steers input incident beams, launched in a first direction along a bottom wave guide layer, to an elevated output wave guide layer via vertical coupling where the beams are steered in a second direction, which is preferably orthogonal to the first direction. The beams are then coupled to output fibers without passing through any additional transition or cross nodes and incurring additional losses.
In a preferred embodiment, the bottom or input wave guides extend the length of the switch in parallel relation along axes parallel to an x-axis. The top or output wave guides each preferably include a collection channel and a plurality of transition channels and 90-degree ramps. The collection channels extend the width of the switch in parallel relation along axes parallel to a y-axis. At each transition node in the switch, the transition sections of the output wave guide extend in the x-direction a short distance through the transition node. The transition channels are preferably located directly above the input wave guides in parallel spaced relation such that the optical field outside the input waveguides overlaps slightly with the transition channels of the output wave guides and vice versa. The transition nodes include electrodes deposited on the sides of a coupling matrix layer sandwiched between the transition channels and input wave guides. The coupling matrix preferably includes electro-optic material at the transition nodes. The refractive index of the E-O coupling layer material is preferably slightly less than the refractive index of the wave guide layers when no electric field is applied. When an electric field is applied across the electrodes, the refractive index of the coupling layer increases making vertical coupling possible. With vertical coupling, a beam propagating through an input wave guide is able to migrate to the corresponding transition channel of an output wave guide as the beam passes through the transition node. The beam then merges into the corresponding collection channel via the corresponding ramp.
In yet another innovative aspect of the present invention, the switch advantageously comprises two identical functional plates and no moving parts. The top and bottom plates each include an array or matrix of identically sized and shaped transmissive blocks. The transmissive blocks, which preferably comprise identically sized and shaped pyramids, include electrically or magnetically active inclined but stationary optically reflective surfaces, e.g. electro-optical (E-O) mirrors. When assembled, the pyramids on the top plate are preferably positioned above the pyramids on the bottom plate and appropriately shifted to orthogonally line up corresponding reflective surfaces and maintain collimation along the optical path. An intermediate layer, in the form of an optical filter to minimize cross-talk or a coupling layer to couple light beams reflected from a bottom pyramid to a top pyramid, may be sandwiched between the top and bottom plates.
In this configuration, incoming collimated and polarized light beams from input fibers are initially launched in a first direction and then steered vertically 90-degrees in a second direction by E-O mirror surfaces on the lower level transmissive blocks. The beams then propagate to an upper level where they are steered 90-degrees in a third direction by E-O mirror surfaces on the upper level transmissive blocks. The beams are then coupled back into the output fibers of the output channels. Because the plates are identical and orthogonally aligned, the switch may be operated bi-directionally.